This invention relates to a start up control for an engine and more particularly to an improved feedback control system and method for a direct injected internal combustion engine in a start up operation.
In the interest of improving engine performance and particularly fuel efficiency and exhaust emission control, many types of engines now employ fuel injection and/or feedback control of the fuel supply to the engine. Fuel injection has the advantages of permitting the amount of fuel delivered for each cycle of the engine to be adjusted. In addition, by utilizing fuel injection and a feedback control system, it is possible to maintain the desired fuel air ratio under a wide variety of engine running condition.
These features are particularly useful with two cycle engines, although not specifically limited thereto. Because the overlap between the scavenge port and exhaust port opening and closing gives rise to the possibility that unburned hydrocarbons may pass into the atmosphere through the exhaust port. In addition, amounts of exhaust gases remaining in the combustion chamber relatively under light speeds and loads can cause misfiring and eventually unburned hydrocarbons again pass through the atmosphere.
Generally, the fuel injection is performed under a relatively high pressure. For this purpose, two different pumps are provided. One is an electrically driven pressure pump which creates a relatively low pressure such as 3 kg/cm2, while the other is a high pressure, engine driven, positive displacement pump which increases the pressure delivered by the former pump to extremely high pressure such as 50 kg/cm2. However, immediately after commencement of cranking, the high pressure pump cannot supply the desired pressure because a starter motor, which powers the high pressure pump at this stage, cannot give sufficient cranking speeds. In addition, the generated pressure is likely accompanied with undesirable fluctuations because the viscosity of lubricating oil for the high pressure pump varies corresponding to the atmospheric temperatures, engine temperatures and deterioration of the oil in quality. Some conventional engines, thus, generally have an electromagnetic valve bypassing the high pressure pump so that only the primary pump may give pressure for the fuel injection.
However, the pressure that will be developed by the high pressure pump after the start up of an engine greatly differ from the pressure given only by the primary pump during the start up (see the dot-dash-line in FIG. 14). The difference also causes a great difference between both of the initiation and the duration of the fuel injection during and after the start up. As a result, the engine cannot start very smoothly and this gives the operator an uneasy feeling.
Also, a relatively large size of sprayed particles under the lower pressure condition gives rise to misfiring (see the relationship between the size of the sprayed fuel and the fuel pressure shown in FIG. 16) and hence the start up time cannot be shortened. Further, since the primary pump only allows fuel injectors to spray a small amount of fuel per unit time, a long duration and an early initiation are required. Accordingly, hydrocarbons and other undesirable substances tend to be discharged to the atmosphere.
Further, the high pressure pump cannot supply sufficient fuel at the commencement of cranking. Due to this nature, if the feedback control demands the high pressure pump to increase the amount of fuel, the pressure generated by the pump may have fluctuations and then relatively long time for cranking may be necessary, because the larger the amount of fuel, the faster the fuel pressure deteriorates (see FIG. 17).
Particularly, in two cycle engines, the fuel injection should be initiated during a limited period for preventing injected fuel from passing through the exhaust port and due to the short time of sprayed fuel diffusion in comparison with four cycle engines. Thus, it is a significant matter how to raise the pressure of injected fuel at the commencement of cranking.
The problem is particularly acute in connection with marine applications because the exhaust gases may be discharged to the atmosphere through the body of water in which the watercraft is operating for silencing purposes. The water level can change due to boat motion, changes in both velocity and other factors. In addition, the trim angle and height of the propulsion unit may be altered. This also will change the back pressure. Accordingly, the combustion conditions tend to be inferior and an increase in the fuel pressure at the commencement of cranking is necessary.
It is, therefore, a principal object of this invention to provide an improved engine feedback control system and particularly a start up operation for the system.
It is a further object of this invention to provide an improved engine feedback control system and method for feedback control engines wherein proper injections of fuel are provided at all times even under the unstable fuel pressure conditions in the start up operation. Also the fuel pressure can be raised so that the engine starts smoothly without giving an operator an uneasy feeling and also improve exhaust emissions.
This invention is adapted to be embodied in a direct cylinder injected, internal combustion engine having an engine body defining at least one cylinder bore in which a piston reciprocates. A cylinder head is affixed to one end of the engine body for closing the cylinder bore and defining with the piston and the cylinder bore a combustion chamber. At least one intake port is provided for admitting an air charge to the combustion chamber. At least one exhaust port is provided for discharging burned combustion products from the combustion chamber. A fuel injector is provided for spraying fuel directly into the combustion chamber for combustion therein. A fuel pump is provided for supplying the fuel to the fuel injector. Means are provided for sensing the pressure of fuel supplied by the fuel pump. A feedback control system adjusts at least initiation of the fuel injection based upon the output from the fuel pressure sensing means.
In accordance with a method of practicing the invention, the pressure of fuel supplied by the fuel pump is sensed. During the time the condition is sensed, at least initiation of the fuel injection is adjusted.